The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Internal combustion engines can use camless variable valve actuation systems including fully flexible valve actuation (FFVA) systems. A valvetrain system including fully flexible valve actuation provides full-range control of engine valve open duration, engine valve open phasing relative to crankshaft rotation, and magnitude of engine valve lift from fully closed to fully open without depending upon the contours of a cam surface. Electrically or hydraulically controlled fully flexible valve actuation systems may enable valves to open multiple times during an engine cycle, or not at all, such as during cylinder deactivation events.
Internal combustion engine controls include time-domain based elements and crank angle-domain based elements related to engine dynamics. Time-domain based engine dynamics can be described using differential equations (linear or nonlinear), whereas the crank angle-based dynamics can be described using rates of change relative to crank angle. Therefore, crank angle based dynamics correspond to crank angle rotation and not time. When engine speed is constant, time-domain based engine dynamics synchronize with crank angle-domain based engine dynamics. Control modules and controllers perform control tasks in both fixed time intervals (i.e., time-based controls) and fixed crank-angle intervals (i.e., event-based controls) to jointly control and monitor various engine operations. For example, sensors and actuators used in engine applications are mostly time-domain based systems. However, engine flow and combustion interactions with the sensors and actuators are crank angle-based.
Control of variable valve actuation systems including fully flexible valve actuation systems entails opening and closing of intake and exhaust engine valves at predetermined profiles as a function of crank-angle preferably repeatable at 720-degree crank angle iterations. Due to this repetitive nature, a repetitive controller can be used to control the fully flexible valve actuation system with high precision. Furthermore, due to the time-based nature of its dynamics, control of the fully flexible valve actuation system is time-domain based. However, during powertrain operation it is preferable for valve actuation to coincide with particular crank angles, in order to synchronize with fuel injection, spark, and combustion timing. Therefore, conversion between control in the time-domain and the crank angle-domain is desirable. Valve actuation can become non-periodic with respect to time, e.g., when the engine speed fluctuates. Inexact conversion from a time-domain based control to a crank angle-domain based control can cause undesirable engine valve motion resulting in poor combustion. Therefore, it would be advantageous to compensate for the non-periodic disturbances in the valvetrain control system for repetitive tasks such as opening and closing of intake and exhaust engine valves at a constant profile as a function of crank-angle that repeats every 720-degree crank angles.